A central tire inflation system offers an advantage to vehicles whose service requirements call for operation on varying terrain, e.g. soft sand, snow, cross-country or hard surface roads. This system generally provides for inflation or deflation of the vehicle tires according to the entry of a control signal by the vehicle operator. The control signal is pneumatically or electronically communicated to the system and the tires are appropriately charged or vented with air routed through the wheel end assembly associated with each tire.
One of the design problems inherent in central tire inflation systems is the need for a reliable seal in the wheel assembly between rotating and non-rotating members. A number of design considerations associated with this problem are discussed in columns 1 and 2 of U.S. Pat. No. 4,470,506, assigned to the assignee of the present invention.
Moreover, it can be quite costly to retrofit a standard production wheel end assembly with an air passage for a central tire inflation system and meet the foregoing criteria. More particularly, this may, in some cases, require the removal of the wheel to permit fitting of the axle spindle with additional internal componentry, as well as machining operations, such as rifle drilling, to adapt the production assembly for central tire inflation.
An example of one design proposal for a rotary seal assembly for a central tire inflation system is shown in U.S. Pat. No. 4,434,833. Specifically, with reference to FIG. 5, a rotary seal assembly includes two air seal lips which are press fit against the surface of an annular ring. However, the practicability of this design is subject to the integrity of the air seal obtained by the press fitting of the air seal lips. Any press fitting of seal members in a dynamic operating environment is adversely affected by variations in seal dimensions, misalignment of seals during assembly, and wear and disturbance of the seals over their operating life. Thus, the design of U.S. Pat. No. 4,434,833 is felt to be attended by these limitations.